<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>是兄弟就来砍我</title>
</head>
<body>
<div id="add">
  <div class="close">

  </div>

</div>

</body>
<style>
  #add {
    position: fixed;
    right: 5px;
    bottom: 5px;
    width: 200px;
    height: 400px;
    border: 1px solid black;
  }
  .close {
    position: absolute;
    top: 0;
    right: 0;
    width: 20px;
    height: 20px;
    border: 1px solid red;
    background-color: #ffcccc;
  }
</style>
</html>